Test 08-object-prototype-stack.p

Source of programm

# 0bject oriented programming with prototypes: stack class

sub makestack()

 # constructor of object makes a hash table; the methods of the object are has table entries where the value is a function without name (aka lambda)
 # data members are also table entries; it is good practice to declare data members in the hash.

 return { 
          'stack' : [], #{},
          

          # when a function is inserted into a collection (hash or vector) then a function object is created.
          # the function object has a this symbol that points to the enclosing collection; so a function can access
          # members of the collection as 'member data' via this . name_of_data_member

          'push' : sub ( top ) 

                  push( ~array this.stack ~top top )
                  println( ~msg 'push: has [ size( ~arg this . stack ) ] elements' )
             
          end,

          'pop' : sub () 

                if size( ~arg this.stack ) == 0
                     println( ~msg 'Error: empty stack' )
                     return Null
                  else 
                     println( ~msg 'pop: has [ size( ~arg this.stack ) ] elements' )
                     return pop ( ~array this . stack )
                  end
   
          end
  }

end


stack = makestack()

stack.push( ~top 1 )
stack.push( ~top 2 )
stack.push( ~top 3 )


i = 1
while i <= 4
  println ( ~msg 'pop: result is [ stack.pop() ]' )
  i = i + 1
end

Standard output for 08-object-prototype-stack.p

push: has 1 elements
push: has 2 elements
push: has 3 elements
pop: has 3 elements
pop: result is 3
pop: has 2 elements
pop: result is 2
pop: has 1 elements
pop: result is 1
Error: empty stack
pop: result is 

Trace output for 08-object-prototype-stack.p

039|... = makestack(  )...
008| return { 'stack' : [ ]  , 'push' : sub (~top) , 'pop' : sub () }
039|stack = makestack(  ):{ 'pop' : sub , 'push' : sub , 'stack' : -> [  ] }
041|stack{'push'}:sub ( ~top 1 )...
018| push( ~array this{'stack'}:[  ] ~top top:1 )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1 ] )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1 ] ):1 .. ' elements' )...
042|stack{'push'}:sub ( ~top 2 )...
018| push( ~array this{'stack'}:[ -> 1 ] ~top top:2 )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2 ] )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2 ] ):2 .. ' elements' )...
043|stack{'push'}:sub ( ~top 3 )...
018| push( ~array this{'stack'}:[ -> 1, -> 2 ] ~top top:3 )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] )...
019| println( ~msg 'push: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] ):3 .. ' elements' )...
046|i = 1
047|while (i:1 <= 4):true
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  )...
025|  if (size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] )...
025|  if (size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] ):3 == 0):false
027|  else
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] )...
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2, -> 3 ] ):3 .. ' elements' )...
030|   return pop( ~array this{'stack'}:[ -> 1, -> 2, -> 3 ] )...
030|   return pop( ~array this{'stack'}:[ -> 1, -> 2, -> 3 ] ):-> 3
030|  end # if
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  ):-> 3 .. '' )...
049| i = (i:1 + 1):2
050|end
047|while (i:2 <= 4):true
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  )...
025|  if (size( ~arg this{'stack'}:[ -> 1, -> 2 ] )...
025|  if (size( ~arg this{'stack'}:[ -> 1, -> 2 ] ):2 == 0):false
027|  else
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2 ] )...
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1, -> 2 ] ):2 .. ' elements' )...
030|   return pop( ~array this{'stack'}:[ -> 1, -> 2 ] )...
030|   return pop( ~array this{'stack'}:[ -> 1, -> 2 ] ):-> 2
030|  end # if
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  ):-> 2 .. '' )...
049| i = (i:2 + 1):3
050|end
047|while (i:3 <= 4):true
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  )...
025|  if (size( ~arg this{'stack'}:[ -> 1 ] )...
025|  if (size( ~arg this{'stack'}:[ -> 1 ] ):1 == 0):false
027|  else
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1 ] )...
029|   println( ~msg 'pop: has ' .. size( ~arg this{'stack'}:[ -> 1 ] ):1 .. ' elements' )...
030|   return pop( ~array this{'stack'}:[ -> 1 ] )...
030|   return pop( ~array this{'stack'}:[ -> 1 ] ):-> 1
030|  end # if
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  ):-> 1 .. '' )...
049| i = (i:3 + 1):4
050|end
047|while (i:4 <= 4):true
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  )...
025|  if (size( ~arg this{'stack'}:[  ] )...
025|  if (size( ~arg this{'stack'}:[  ] ):0 == 0):true
026|   println( ~msg 'Error: empty stack' )...
027|   return Null
027|  end # if
048| println( ~msg 'pop: result is ' .. stack{'pop'}:sub (  ):Null .. '' )...
049| i = (i:4 + 1):5
050|end
047|while (i:5 <= 4):false
050|end # finish loop